Method for fabricating a Schottky diode including a guard ring overlapping an insolation layer

ABSTRACT

A Schottky diode includes a deep well formed in a substrate, an isolation layer formed in the substrate, a first conductive type guard ring formed in the deep well along an outer sidewall of the isolation layer and located at a left side of the isolation layer, a second conductive type well formed in the deep well along the outer sidewall of the isolation layer and located at a right side of the isolation layer, an anode electrode formed over the substrate and coupled to the deep well and the guard ring, and a cathode electrode formed over the substrate and coupled to the well. A part of the guard ring overlaps the isolation layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2010-0027059, filed on Mar. 26, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

Exemplary embodiments of the present invention relate to a technology offabricating a semiconductor device, and more particularly, to a Schottkydiode and a method for fabricating the same.

A Schottky diode mainly used as a switching element or a rectificationelement in a semiconductor device uses a metal-semiconductor junctionand has superior high speed switching characteristics as compared with ageneral PN junction diode. This is because minority carrier injection(MCI) does not occur when a forward voltage is applied to the Schottkydiode, differently from the PN junction diode. In the case of theSchottky diode, a current flows by majority carriers instead of minoritycarriers. Therefore, the Schottky diode has an advantage that a reverserecovery time is very short because there is no accumulation effect.However, the Schottky diode has a disadvantage that it is difficult tocontrol a high current (or a high voltage) because a current flows bymajority carriers. In this regard, recently, a Schottky diode isextensively used, which includes a guard ring in order to achieve highspeed switching characteristics and simultaneously control a largecurrent.

FIG. 1 is a cross-sectional view illustrating a Schottky diode inaccordance with a first prior art, and FIGS. 2A and 2B are diagramsillustrating the problem of the Schottky diode in accordance with thefirst prior art.

Hereinafter, the Schottky diode in accordance with the first prior artwill be described with reference to FIG. 1. The Schottky diode includesan N type deep well 12 formed in a substrate 11, an isolation layer 22formed in the substrate 11, an N type well 16, a cathode electrode 17coupled to the well 16, a P type guard ring 20, and an anode electrode21 coupled to the deep well 12 and the guard ring 20. The N type well 16is formed in the deep well 12 and is located at the right side of theisolation layer 22. The guard ring 20 is formed in the deep well 12 andis located at the left side of the isolation layer 22 while being spacedapart from the isolation layer 22 by a predetermined interval. The guardring 20 includes a P-type first impurity region 19 formed on the surfaceof the substrate 11, and a P-type second impurity region 18 formed underthe P-type first impurity region 19 having an impurity dopingconcentration lower than that of the first impurity region 19.

As indicated by reference numeral A of FIG. 1, which illustrates theSchottky diode in accordance with the first prior art, and referencenumeral A of FIG. 2A which is a simulation image illustrating stressconcentration, since the guard ring 20 is spaced apart from theisolation layer 22 by the predetermined interval, it is problematic inthat stress is concentrated between the isolation layer 22 and the guardring 20. When the stress is concentrated between the isolation layer 22and the guard ring 20, a leakage current may easily flow through astress concentration point. In the case of fabricating the Schottkydiode in accordance with the first prior art, it may be difficult tocontrol the interval between the isolation layer 22 and the guard ring20, large variation in a leakage current value may occur according todies/wafers or dies/lots.

Furthermore, as indicated by reference numeral B of FIG. 1, whichillustrates the Schottky diode in accordance with the first prior art,and the graph of FIG. 2B which illustrates a reverse bias current (thatis, a leakage current) according to dies on a wafer, the guard ring 20includes the first impurity region 19 having an impurity dopingconcentration very higher than that of the deep well 12, the leakagecurrent due to the big difference between the impurity dopingconcentrations of the deep well 12 and the first impurity region 19 mayoccur. In relation to the leakage current, large variation in theleakage current value may occur according to dies/wafers. In addition,due to the big difference between the impurity doping concentrations ofthe deep well 12 and the first impurity region 19, a breakdown voltageof the Schottky diode, that is, the ability of withstanding a highvoltage (or a high current) may be reduced. For reference, (A) of FIG.2B is a diagram illustrating the position of dies on a wafer and (B) ofFIG. 2B is a current-voltage graph illustrating a leakage currentgenerated in each die when a reverse bias is applied to the Schottkydiode in accordance with the first prior art.

In order to solve the above problems in accordance with the first priorart, a Schottky diode in accordance with a second prior art has beenproposed.

FIG. 3 is a cross-sectional view illustrating the Schottky diode inaccordance with the second prior art.

Hereinafter, the Schottky diode in accordance with the second prior artwill be described with reference to FIG. 3. The Schottky diode includesan N type deep well 32 formed in a substrate 31, an isolation layer 42formed in the substrate 31, an N well 36, a cathode electrode 37 coupledto the well 36, a P well 40, and an anode electrode 41 coupled to thedeep well 32 and the P well 40. The N well 36 is formed in the deep well32 and is located at the right side of the isolation layer 42. The Pwell 40 is formed in the deep well 32 and is located at the left side ofthe isolation layer 42 while being in contact with the N well 36 and theisolation layer 42. The P well 40 serves as a guard ring, and has animpurity doping concentration lower than that of the first impurityregion 19 in accordance with the first prior art.

In accordance with the second prior art, as compared with the firstprior art, stress is not concentrated between the isolation layer 42 andthe P well 40 serving as the guard ring because the isolation layer 42is in contact with the P well 40 (see reference numeral A of FIG. 3 andFIG. 4A), and the generation of a leakage current due to the bigdifference between the impurity doping concentrations of the deep well32 and the P well 40 may be reduced because the P well 40 has animpurity doping concentration lower than that of the guard ring 20 inaccordance with the first prior art. For reference, FIG. 4A is asimulation image illustrating stress concentration between the isolationlayer and the guard ring, and is a comparison image of the first priorart and the second prior art.

However, in the Schottky diode in accordance with the second prior art,as shown in reference numeral C of FIG. 3 and FIG. 4A, stress isconcentrated at the boundary surface of the N well 36 and the P well 40,resulting in the reduction of the breakdown voltage of the Schottkydiode. For reference, FIG. 4B is a current-voltage graph illustrating acomparison of the breakdown voltage of the Schottky diode in accordancewith the first prior art and the breakdown voltage of the Schottky diodein accordance with the second prior art. Referring to FIG. 4B, it may beunderstood that the breakdown voltage of the Schottky diode inaccordance with the first prior art is approximately 25.3 V, but thebreakdown voltage of the Schottky diode in accordance with the secondprior art is reduced to approximately 21.6 V.

Furthermore, in accordance with the second prior art, as shown inreference numeral B of FIG. 3 and FIGS. 4C and 4D, since the P well 40serving as the guard ring is coupled to the N well 36 coupled to thecathode electrode 37, the current path from the anode electrode 41 tothe cathode electrode 37 is increased (or lengthened) as compared withthe first prior art, resulting in the deterioration of the forwardcharacteristics of the Schottky diode. For reference, FIG. 4C is animage illustrating a comparison of the current path of the Schottkydiode in accordance with the first prior art and the current path of theSchottky diode in accordance with the second prior art. FIG. 4D is acurrent-voltage graph illustrating the forward characteristics of theSchottky diode in accordance with the first prior art and the Schottkydiode in accordance with the second prior art.

In brief, it is necessary to provide a Schottky diode capable ofensuring forward characteristics, leakage current characteristics, andbreakdown voltage characteristics and simultaneously achieving uniformcharacteristics according to dies/wafers, and a method for fabricatingthe same.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to provide a Schottkydiode capable of ensuring forward characteristics, leakage currentcharacteristics, and breakdown voltage characteristics andsimultaneously achieving uniform characteristics according todies/wafers, and a method for fabricating the same.

In accordance with an embodiment of the present invention, a Schottkydiode includes: a deep well formed in a substrate; an isolation layerformed in the substrate; a first conductive type guard ring formed inthe deep well along an outer sidewall of the isolation layer and locatedat a left side of the isolation layer; a second conductive type wellformed in the deep well along the outer sidewall of the isolation layerand located at a right side of the isolation layer; an anode electrodeformed over the substrate and coupled to the deep well and the guardring; and a cathode electrode formed over the substrate and coupled tothe well, wherein a part of the guard ring overlaps the isolation layer.

The isolation layer may have a ring shape.

The guard ring may have a depth smaller than a depth of the isolationlayer on a basis of an upper surface of the substrate.

The isolation layer may have a depth smaller than a depth of the well onthe basis of the upper surface of the substrate. The lower portion ofthe well may surround a part of a lower surface of the isolation layer.

An impurity doping concentration of the well may be reduced in a depthdirection from a surface of the substrate. The well may include: asecond conductive type third impurity region being in contact with thecathode electrode; a second conductive type second impurity regionformed on a lower portion of the third impurity region; and a secondconductive type first impurity region formed on a lower portion of thesecond impurity region, wherein the third impurity region may have thehighest impurity doping concentration and the first impurity region mayhave the lowest impurity doping concentration.

The anode electrode and the cathode electrode may include a metalsilicide layer.

The first conductive type and the second conductive type may becomplementary to each other, the first conductive type may be a P type,and the second conductive type may be an N type.

In accordance with another embodiment of the present invention, a methodfor fabricating a Schottky diode includes: forming an isolation layerhaving a ring shape in a substrate in which a second conductive typedeep well is formed; forming a second conductive type well in the deepwell along an outer sidewall of the isolation layer to be located at aright side of the isolation layer; forming a first conductive type guardring in the deep well along the outer sidewall of the isolation layer tobe located at a left side of the isolation layer in such a manner that apart of the guard ring overlaps the isolation layer; and forming ananode electrode over the substrate to be coupled to the deep well andthe guard ring and simultaneously forming a cathode electrode coupled tothe well over the substrate.

The isolation layer may be formed to have a ring shape.

The guard ring may have a depth smaller than a depth of the isolationlayer.

The well may have a depth larger than a depth of the isolation layer. Alower portion of the well may surround a part of a lower surface of theisolation layer.

An impurity doping concentration of the well may be reduced in a depthdirection from a surface of the substrate. The forming of the well mayinclude: forming an ion implantation mask over the substrate to exposethe deep well of an outer side of the isolation layer; forming a firstimpurity region in the deep well by ion-implanting a second conductivetype impurity by using the ion implantation mask as an ion implantationbarrier; forming a second impurity region on an upper portion of thefirst impurity region by ion-implanting the second conductive typeimpurity by using the ion implantation mask as an ion implantationbarrier, the second impurity region having an impurity dopingconcentration higher than an impurity doping concentration of the firstimpurity region; and forming a third impurity region on an upper portionof the second impurity region by ion-implanting the second conductivetype impurity by using the ion implantation mask as an ion implantationbarrier, the third impurity region having an impurity dopingconcentration higher than an impurity doping concentration of the secondimpurity region.

The forming of the guard ring may include: forming an ion implantationmask over the substrate to expose the deep well of the left side of theisolation layer and a part of the isolation layer being in contact withthe deep well; and ion-implanting a first conductive type impurity byusing the ion implantation mask as an ion implantation barrier.

The forming of the anode electrode and the cathode electrode mayinclude: depositing a metal layer over a resultant structure includingthe substrate; forming a metal silicide layer by reacting the substratewith the metal layer through a thermal treatment process; and removing ametal layer which does not react in the thermal treatment process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a Schottky diode inaccordance with a first prior art.

FIG. 2A is a simulation image illustrating stress concentration betweenan isolation layer and a guard ring of a Schottky diode in accordancewith a first prior art.

FIG. 2B is a current-voltage graph illustrating leakage currentcharacteristics according to dies of a Schottky diode in accordance witha first prior art.

FIG. 3 is a cross-sectional view illustrating a Schottky diode inaccordance with a second prior art.

FIG. 4A is an image illustrating stress concentration between anisolation layer and a guard ring, and is a comparison image of aSchottky diode in accordance with a first prior art and a Schottky diodein accordance with a second prior art.

FIG. 4B is a current-voltage graph illustrating a comparison of abreakdown voltage of a Schottky diode in accordance with a first priorart and a breakdown voltage of a Schottky diode in accordance with asecond prior art.

FIG. 4C is an image illustrating a comparison of a current path betweenan anode electrode and a cathode electrode in a Schottky diode inaccordance with a first prior art and a current path between an anodeelectrode and a cathode electrode in a Schottky diode in accordance witha second prior art.

FIG. 4D is a current-voltage graph illustrating forward characteristicsof a Schottky diode in accordance with a first prior art and a Schottkydiode in accordance with a second prior art.

FIG. 5A is a plan view illustrating a Schottky diode in accordance withone embodiment of the present invention.

FIG. 5B is a cross-sectional view of a Schottky diode in accordance withone embodiment of the present invention, which is taken along line X-X′shown in FIG. 5A.

FIGS. 6B to 6E are cross-sectional views illustrating a method forfabricating a Schottky diode in accordance with one embodiment of thepresent invention, which is taken along line X-X′ shown in FIG. 5A.

FIGS. 7A to 7D are cross-sectional views illustrating Schottky diodesfor comparison, wherein FIG. 7A is a cross-sectional view illustrating aSchottky diode in accordance with a first prior art, FIG. 7B is across-sectional view illustrating a Schottky diode in accordance with asecond prior art (1), FIG. 7C is a cross-sectional view illustrating aSchottky diode in accordance with a second prior art (2), and FIG. 7D isa cross-sectional view illustrating a Schottky diode in accordance withone embodiment of the present invention.

FIG. 8A is a wafer map illustrating the distribution of dies on a waferin which the characteristics of Schottky diodes in accordance with theprior arts and one embodiment of the present invention are measured.

FIGS. 8B to 8G are graphs illustrating the characteristics of Schottkydiodes in accordance with the prior arts and one embodiment of thepresent invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present inventionto those skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to a casewhere the first layer is formed directly on the second layer or thesubstrate but also a case where a third layer exists between the firstlayer and the second layer or the substrate.

The embodiment of the present invention provides a Schottky diodecapable of ensuring forward characteristics, leakage currentcharacteristics, and breakdown voltage characteristics andsimultaneously allowing these characteristics to be uniform according todies/wafers, and a method for fabricating the same.

In accordance with an embodiment of the present invention, a firstconductive type and a second conductive type are complementary to eachother, the first conductive type is a P type and the second conductivetype is an N type. Of course, when the first conductive type is an Ntype, the second conductive type may be a P type.

FIGS. 5A and 5B are diagrams illustrating a Schottky diode in accordancewith the embodiment of the present invention, wherein FIG. 5A is a planview illustrating the Schottky diode and FIG. 5B is a cross-sectionalview taken along line X-X′ shown in FIG. 5A.

Referring to FIGS. 5A and 5B, the Schottky diode in accordance with theembodiment of the present invention includes a second conductive typedeep well 52 formed in a substrate 51, an isolation layer 62 formed inthe substrate 51 and having a ring shape, a first conductive type guardring 60, a second conductive type well 56, an anode electrode 61, and acathode electrode 57. The first conductive type guard ring 60 is formedin the deep well 52 along the outer sidewall of the isolation layer 62and is located at the left side of the isolation layer 62. The secondconductive type well 56 is formed in the deep well 52 along the outersidewall of the isolation layer 62 and is located at the right side ofthe isolation layer 62. The anode electrode 61 is formed on thesubstrate 51 and coupled to the deep well 52 and the guard ring 60. Thecathode electrode 57 is formed on the substrate 51 and coupled to thewell 56. The Schottky diode in accordance with the embodiment of thepresent invention is characterized in that a part of the guard ring 60overlaps the isolation layer 62.

The guard ring 60 partially overlapping the isolation layer 62 is animpurity region formed by ion-implanting an impurity into the substrate51. The overlap structure of the guard ring 60 and the isolation layer62 is achieved by forming the guard ring 60 by using an ion implantationmask which simultaneously exposes a part of the deep well 52 and a partof an inner side of the isolation layer 62 being in contact with thedeep well 52. This is for substantially preventing stress from beingconcentrated between the isolation layer 62 and the guard ring 60 byforming a contact structure of the isolation layer 62 and the guard ring60 even if a process error occurs in the process of forming the guardring 60, for example, the ion implantation mask is misaligned.

Furthermore, in order to suppress the generation of a leakage currentdue to the difference between the impurity doping concentrations of thedeep well 52 and the guard ring 60 and simultaneously substantiallyprevent a breakdown voltage of the Schottky diode from being reduced bythe guard ring 60, the guard ring 60 may be formed such that thedifference between the impurity doping concentrations of the deep well52 and the guard ring 60 is minimized if the characteristics of theguard ring 60 may be ensured. As one example, the guard ring 60 may havean impurity doping concentration of approximately 1×10¹⁹ atoms/cm³ toapproximately 5×10²⁰ atoms/cm³, and the deep well 52 may have animpurity doping concentration of approximately 1×10¹⁴ atoms/cm³ toapproximately 1×10¹⁹ atoms/cm³. For reference, when it is assumed thatthe impurity doping concentration of the deep well 52 is constant, theguard ring in accordance with the first prior art and the guard ring inaccordance with the second prior art have an impurity dopingconcentration of 10²¹ atoms/cm³ or more. That is, the guard rings inaccordance with the prior arts have an impurity doping concentrationhigher than that of the guard ring 60 in accordance with the embodimentof the present invention.

The guard ring 60 may have a depth smaller than that of the isolationlayer 62 on the basis of the upper surface of the substrate 51. This isfor substantially preventing the forward characteristics of the Schottkydiode from being deteriorated due to the increase in a current path fromthe anode electrode 61 to the cathode electrode 57.

The well 56 may have a depth larger than that of the isolation layer 62on the basis of the upper surface of the substrate 51. This is forfacilitating the formation of the current path between the anodeelectrode 61 and the cathode electrode 57, that is, for improving theforward characteristics of the Schottky diode. For example, when thewell 56 has a depth smaller than that of the isolation layer 62 on thebasis of the upper surface of the substrate 51, since the current pathfrom the anode electrode 61 to the cathode electrode 57 is increased,the forward characteristics of the Schottky diode may be deteriorated.

In addition, in order to improve the forward characteristics of theSchottky diode, the lower portion of the well 56 may surround a part ofa lower surface of the isolation layer 62.

The well 56 coupled to the cathode electrode 57 includes a secondconductive-type first impurity region 53, a second conductive-type thirdimpurity region 55, and a second conductive-type second impurity region54. The second conductive-type first impurity region 53 has a depthlarger than that of the isolation layer 62 on the basis of the uppersurface of the substrate 51. The second conductive-type third impurityregion 55 is formed on the surface of the substrate 51 and is in contactwith the cathode electrode 57. The second conductive-type secondimpurity region 54 is interposed between the first impurity region 53and the third impurity region 55. That is, the well 56 has a structurein which the third impurity region 55, the second impurity region 54,and the first impurity region 53 are sequentially stacked in the depthdirection from the surface of the substrate 51. The impurity dopingconcentration of the well 56 may be reduced in the depth direction fromthe surface of the substrate 51 in order to improve the breakdownvoltage and the forward characteristics of the Schottky diode andsimultaneously reduce a contact resistance with the cathode electrode57. As one example, the first impurity region 53 may have an impuritydoping concentration of approximately 1×10¹⁴ atoms/cm³ to approximately1×10¹⁹ atoms/cm³, the second impurity region 54 may have an impuritydoping concentration of approximately 1×10¹⁹ atoms/cm³ to approximately5×10²⁰ atoms/cm³, and the third impurity region 55 may have an impuritydoping concentration of approximately 5×10²⁰ atoms/cm³ to approximately5×10²¹ atoms/cm³.

The substrate 21 may include a silicon substrate, and the anodeelectrode 61 and the cathode electrode 57 may include a metal silicidelayer, for example, a cobalt silicide layer CoSi. The isolation layer 62may be formed through a shallow trench isolation (STI) process.Furthermore, the isolation layer 62 includes a ring-shaped isolationlayer, which is located between the guard ring 60 and the well 56 toelectrically isolate the guard ring 60 from the well 56, and anisolation layer which surrounds the whole of the Schottky diodeincluding the well 56.

The Schottky diode having the above structure in accordance with theembodiment of the present invention may ensure the forwardcharacteristics, backward characteristics (or leakage currentcharacteristics), and breakdown voltage characteristics andsimultaneously allow these characteristics to be uniform according todies/wafers (see FIGS. 7A to 7D and FIGS. 8A to 8G).

In detail, in the Schottky diode in accordance with the embodiment ofthe present invention, since the guard ring 60 has a depth smaller thanthat of the isolation layer 62 and the well 56 coupled to the cathodeelectrode 57 has a depth larger than that of the isolation layer 62 onthe basis of the upper surface of the substrate 51, the current pathbetween the anode electrode 61 and the cathode electrode 57 issubstantially prevented from being increased, resulting in theimprovement of the forward characteristics of the Schottky diode. Inaddition, the well 56 has a structure in which the first impurity region53, the second impurity region 54, and the third impurity region 55 arestacked such that the impurity doping concentration is reduced in thedepth direction from the surface of the substrate 51, so that theforward characteristics of the Schottky diode may be further improved.

Furthermore, in the Schottky diode in accordance with the embodiment ofthe present invention, since the guard ring 60 partially overlaps theisolation layer 62, stress is substantially prevented from beingconcentrated at a boundary region of the guard ring 60 and the isolationlayer 62, so that the generation of the leakage current due to stressconcentration may be substantially prevented. Furthermore, the guardring 60 and the well 56, which have conductive types complementary toeach other, are not in contact with each other, so that the generationof the leakage current due to stress concentration at an interfacebetween the guard ring 60 and the well 56 may be substantiallyprevented. Furthermore, the difference between the impurity dopingconcentrations of the guard ring 60 and the deep well 52 is minimized,so that the generation of the leakage current due to the differencebetween the impurity doping concentrations thereof may be substantiallyprevented.

Moreover, in the Schottky diode in accordance with the embodiment of thepresent invention, the difference between the impurity dopingconcentrations of the guard ring 60 and the deep well 52 is minimized,so that the reduction in a breakdown voltage of the Schottky diode dueto the difference between the impurity doping concentrations thereof maybe substantially prevented. Moreover, the guard ring 60 and the well 56,which have conductive types complementary to each other, are not incontact with each other, so that the reduction in the breakdown voltageof the Schottky diode may be substantially and effectively prevented.Moreover, the well 56 has a structure in which the first impurity region53, the second impurity region 54, and the third impurity region 55 arestacked such that the impurity doping concentration is reduced in thedepth direction from the surface of the substrate 51, so that thereduction in the breakdown voltage of the Schottky diode may be moresubstantially and more effectively prevented.

In addition, in the Schottky diode in accordance with the embodiment ofthe present invention, the above-described characteristics may be stablyachieved and may be uniform according to dies/wafers. This may be moreclearly understood with reference to FIGS. 8B to 8E.

FIGS. 6B to 6E are cross-sectional views illustrating the method forfabricating the Schottky diode in accordance with the embodiment of thepresent invention, which is taken along line X-X′ shown in FIG. 5A.

Referring to FIG. 6A, the second conductive type deep well 52 is formedby ion-implanting an impurity into the substrate 51. When the secondconductive type is an N type, the deep well 52 may be formed byion-implanting phosphorous (P), arsenic (As) and the like, and may havean impurity doping concentration of approximately 1×10¹⁴ atoms/cm³ toapproximately 1×10¹⁹ atoms/cm³.

The isolation layer 62 having a ring shape is formed on the substrate 51in which the deep well 52 is formed. The isolation layer 62 may beformed through a shallow trench isolation (STI) process. The isolationlayer 62 may include a first isolation layer 62A and a second isolationlayer 62B. The first isolation layer 62A defines an area, in which ananode electrode and a guard ring are to be formed through subsequentprocesses, and has a ring shape. The second isolation layer 62B definesan area, in which a cathode electrode and a well are to be formedthrough subsequent processes, together with the first isolation layer62A, and surrounds the first isolation layer 62A at the outer side ofthe first isolation layer 62A. The second isolation layer 62B alsoisolates an adjacent Schottky diode.

Referring to FIG. 6B, a first ion implantation mask 58 is formed on thesubstrate 51 to expose the deep well 52 between the first isolationlayer 62A and the second isolation layer 62B, that is, the substrate 51including the area in which the cathode electrode is to be formed. Thefirst ion implantation mask 58 may include photo resist (PR).

The second conductive-type first impurity region 53 is formed byion-implanting an impurity into the deep well 52 by using the first ionimplantation mask 58 as an ion implantation barrier. The first impurityregion 53 serves as a part of the well coupled to the cathode electrodethrough subsequent processes.

The first impurity region 53 may have a depth larger than that of theisolation layer 62 on the basis of the upper surface of the substrate 51in order to improve the forward characteristics of the Schottky diode.The depth of the first impurity region 53 may be adjusted throughion-implanting energy. In addition, in order to further improve theforward characteristics of the Schottky diode, the lower portion of thefirst impurity region 53 may surround a part of the lower surface of theisolation layer 62. This may be achieved through a thermal treatmentprocess for activating the first impurity region 53, and by taking thedegree of diffusion of the impurity according to the thermal treatmentprocess into consideration.

In order to improve the breakdown voltage of the Schottky diode, thefirst impurity region 53 may have an impurity doping concentrationsimilar to that of the deep well 52, for example, an impurity dopingconcentration of approximately 1×10¹⁴ atoms/cm³ to approximately 1×10¹⁹atoms/cm³.

Referring to FIG. 6C, after the first impurity region 53 is formed byusing the first ion implantation mask 58 as the ion implantationbarrier, the second conductive-type second impurity region 54 and thesecond conductive-type third impurity region 55 are formed in the firstimpurity region 53. In such a case, on the basis of the upper surface ofthe substrate 51, the first impurity region 53 has the largest depth,the third impurity region 55 has the smallest depth, and the secondimpurity region 54 is located between the first impurity region 53 andthe third impurity region 55.

The second impurity region 54 may have an impurity doping concentrationof approximately 1×10¹⁹ atoms/cm³ to approximately 5×10²⁰ atoms/cm³, andthe third impurity region 55 may have an impurity doping concentrationof approximately 5×10²⁰ atoms/cm³ to approximately 5×10²¹ atoms/cm³. Thedepths of the second impurity region 54 and the third impurity region 55may be adjusted through ion implantation energy.

Through the above-described processes, it may be possible to form thesecond conductive-type well 56 having the stack structure of the firstimpurity region 53, the second impurity region 54 and the third impurityregion 55.

Referring to FIG. 6D, the first ion implantation mask 58 is removed, anda second ion implantation mask 59 is formed on the substrate 51 toexpose the area in which the guard ring is to be formed. The second ionimplantation mask 59 may have an opening which exposes a part of aninner side of the isolation layer 62 (that is, a part of an inner sideof the isolation layer 62A) and a part of the deep well 52 being incontact with an outer sidewall of the isolation layer 62A. The secondion implantation mask 59 may include photo resist (PR).

The reason for forming the second ion implantation mask 59 such that theopening thereof exposes the part of the inner side of the isolationlayer 62 is to substantially prevent a process error, for example, tosubstantially prevent the guard ring to be formed through subsequentprocesses from being spaced apart from the isolation layer 62 due tomisalignment.

The first conductive type guard ring 60 is formed by ion-implanting animpurity into the deep well 52 by using the second ion implantation mask59 as an ion implantation barrier. The guard ring 60 may be formed tohave a depth smaller than that of the isolation layer 62 on the basis ofthe upper surface of the substrate 51 in order to improve the forwardcharacteristics of the Schottky diode.

Furthermore, the guard ring 60 may be formed such that the differencebetween the impurity doping concentrations of the guard ring 60 and thedeep well 52 is minimized in order to ensure the breakdown voltagecharacteristics and the leakage current characteristics the Schottkydiode. For example, the guard ring 60 may have an impurity dopingconcentration of approximately 1×10¹⁹ atoms/cm³ to approximately 5×10²⁰atoms/cm³.

Referring to FIG. 6E, the second ion implantation mask 59 is removed,and a metal layer (not shown) is deposited on a resultant structureincluding the substrate 51 in order to form the anode electrode 61 andthe cathode electrode 57. The metal layer is subject to a thermaltreatment process to simultaneously form the anode electrode 61 and thecathode electrode 57, which include a silicide layer, through a reactionbetween the substrate 51 (for example, a silicon substrate) and themetal layer. A remaining metal layer, which does not react during thethermal treatment process, is removed.

The anode electrode 61 covers a resultant structure including thesubstrate 51 between the isolation layers 62 and may be coupled to thedeep well 52 and the guard ring 60. The cathode electrode 57 is locatedat an outer side of the isolation layers 62 and above the isolationlayers 62, and may be coupled to the well 56.

Through the above-described processes, the Schottky diode in accordancewith the embodiment of the present invention may be formed.

Hereinafter, the characteristics of the Schottky diode in accordancewith the embodiment of the present invention will be described indetail. In order to facilitate the understanding of the characteristicsof the Schottky diode in accordance with the embodiment of the presentinvention, a comparison with the characteristics of the Schottky diodein accordance with the first prior art and the second prior art is used.

FIG. 7A is a cross-sectional view illustrating the Schottky diode inaccordance with the first prior art, FIGS. 7B and 7C are cross-sectionalviews illustrating the Schottky diode in accordance with the first priorart, and FIG. 7D is a cross-sectional view illustrating the Schottkydiode in accordance with the embodiment of the present invention. FIGS.7A to 7D illustrate the Schottky diodes fabricated in order to comparethe Schottky diode in accordance with the prior arts with the Schottkydiode in accordance with the embodiment of the present invention, andthe unit of numerical values written at the upper portions of FIGS. 7Ato 7D is μm. The Schottky diode shown in FIG. 7B has the same elementsas those of the Schottky diode shown in FIG. 7C, except for the linewidths among the elements. For the purpose of convenience, the Schottkydiode shown in FIG. 7B will be referred to as “a second prior art (1)”,and the Schottky diode shown in FIG. 7C will be referred to as “a secondprior art (2)”.

FIG. 8A is a wafer map illustrating dies on a wafer in which thecharacteristics of the Schottky diodes are measured, and FIGS. 8B to 8Gare graphs illustrating the characteristics of the Schottky diodes shownin FIGS. 7A to 7D.

When comparing the forward characteristics of the Schottky diodes inaccordance with the prior arts with the forward characteristics of theSchottky diode in accordance with the embodiment of the presentinvention with reference to FIGS. 8B to 8G, it may be understood thatthe Schottky diode in accordance with the embodiment of the presentinvention has the best characteristics. Particularly, in terms of theforward current characteristics, the Schottky diode in accordance withthe embodiment of the present invention has the characteristics improvedby an approximately 40%, as compared with the Schottky diodes inaccordance with the prior arts (when Vf=approximately 0.4V).

This results from the fact that the guard ring 60 has a depth smallerthan that of the isolation layer 62 and the well 56 has a depth largerthan that of the isolation layer 62 on the basis of the upper surface ofthe substrate 51 in the Schottky diode in accordance with the embodimentof the present invention, so that the current path between the anodeelectrode 61 and the cathode electrode 57 may be shortened as comparedwith the prior arts, and the well 56 has a structure in which the firstimpurity region 53, the second impurity region 54, and the thirdimpurity region 55 are stacked such that the impurity dopingconcentration may be reduced in the depth direction from the surface ofthe substrate 51.

When comparing the backward characteristics of the Schottky diodes inaccordance with the prior arts with the backward characteristics of theSchottky diode in accordance with the embodiment of the presentinvention, the similar result (in detail, the backward characteristicsof 50 pA or less) is obtained in both the prior arts and the embodimentof the present invention (when Vr=approximately 15V and approximately20V).

When comparing the breakdown voltage characteristics of the Schottkydiodes in accordance with the prior arts with the breakdown voltagecharacteristics of the Schottky diode in accordance with the embodimentof the present invention, it may be understood that the Schottky diodein accordance with the embodiment of the present invention has the bestcharacteristics (in the sequence of the present invention, the firstprior art, the second prior art (1), and the second prior art (2)).

This results from the fact that the guard ring 60 and the well 56, whichhave conductive types complementary to each other, are spaced apart fromeach other, and the difference between impurity doping concentrations ofthe deep well 52 and the guard ring 60 is minimized in the Schottkydiode in accordance with the embodiment of the present invention, ascompared with the prior arts. Furthermore, This results from the factthat the well 56 has a structure in which the first impurity region 53,the second impurity region 54, and the third impurity region 55 arestacked such that the impurity doping concentration is reduced in thedepth direction from the surface of the substrate 51, so that thedifference between impurity doping concentrations of the deep well 52and the guard ring 60 is minimized.

For reference, the guard ring 60 is provided such that the Schottkydiode controls a high current (or a high voltage). Therefore, when theimpurity doping concentration of the guard ring 60 is reduced for thebreakdown voltage characteristics of the Schottky diode, the forwardcharacteristics and the backward characteristics of the Schottky diodemay be deteriorated. However, as described above, the Schottky diode inaccordance with the embodiment of the present invention may ensure thebreakdown voltage characteristics as well as the forward characteristicsand the backward characteristics.

In terms of variation in the above-described characteristics accordingto dies/wafers in the Schottky diodes in accordance with the prior artsand the Schottky diode in accordance with the embodiment of the presentinvention, it may be understood that the variation according todies/wafers is small in the Schottky diode in accordance with theembodiment of the present invention, as compared with the prior arts.

In brief, in the Schottky diode and the method for fabricating the samein accordance with the embodiment of the present invention, forwardcharacteristics, leakage current characteristics, and breakdown voltagecharacteristics may be ensured and simultaneously the above-describedcharacteristics may be uniform according to dies/wafers.

In accordance with the embodiment of the present invention, since aguard ring has a depth smaller than that of an isolation layer and awell has a depth larger than that of the isolation layer on the basis ofthe upper surface of a substrate, an increase in a current path betweenan anode electrode and a cathode electrode is substantially prevented,resulting in the improvement of the forward characteristics of aSchottky diode.

Furthermore, in accordance with the embodiment of the present invention,first to third impurity regions are stacked such that the impuritydoping concentrations thereof are reduced in the depth direction fromthe surface of the substrate, resulting in the improvement of theforward characteristics of the Schottky diode. In addition, a breakdownvoltage of the Schottky diode may be substantially prevented from beingreduced.

Furthermore, in accordance with the embodiment of the present invention,since the guard ring partially overlaps the isolation layer, stress issubstantially prevented from being concentrated at a boundary region ofthe guard ring and the isolation layer, so that the generation of aleakage current due to stress concentration may be substantiallyprevented.

Furthermore, in accordance with the embodiment of the present invention,the guard ring and the well, which have conductive types complementaryto each other, are not in contact with each other, so that thegeneration of the leakage current due to stress concentration at aninterface between the guard ring and the well may be substantiallyprevented. In addition, the breakdown voltage of the Schottky diode maybe substantially prevented from being reduced.

Furthermore, in accordance with the embodiment of the present invention,the difference between the impurity doping concentrations of the guardring and the deep well is minimized, so that the generation of theleakage current due to the difference between the impurity dopingconcentrations thereof may be substantially prevented. In addition, thebreakdown voltage of the Schottky diode may be substantially preventedfrom being reduced.

Moreover, in accordance with the embodiment of the present invention, itmay be provide the Schottky diode in which the above-describedcharacteristics are uniform according to dies/wafers.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A method for fabricating a Schottky diode,comprising: forming an isolation layer in a substrate in which a deepwell of a second conductive type is formed; forming a well region of asecond conductive type in the deep well along an outer sidewall of theisolation layer to be located at one side of the isolation layer;forming a guard ring of a first conductive type in the deep well alongthe outer sidewall of the isolation layer to be located at an oppositeside of the isolation layer in such a manner that a part of the guardring overlaps the isolation layer; and forming an anode electrode overthe substrate to be coupled to the deep well and the guard ring andsimultaneously forming a cathode electrode coupled to the well regionover the substrate, wherein an impurity doping concentration of the wellregion is reduced in a depth direction from a surface of the substrate,wherein the forming of the well region comprises: forming an ionimplantation mask over the substrate to expose the deep well of an outerside of the isolation layer; forming a first impurity region in the deepwell by ion implanting a second conductive type impurity by using theion implantation mask as an ion implantation barrier; forming a secondimpurity region on an upper portion of the first impurity region byion-implanting the second conductive type impurity by using the ionimplantation mask as an ion implantation barrier, the second impurityregion having an impurity doping concentration higher than an impuritydoping concentration of the first impurity region; and forming a thirdimpurity region on an upper portion of the second impurity region byion-implanting the second conductive type impurity by using the ionimplantation mask as an ion implantation barrier, the third impurityregion having an impurity doping concentration higher than an impuritydoping concentration of the second impurity region.
 2. The method ofclaim 1, wherein the isolation layer is formed to have a ring shape. 3.The method of claim 1, wherein the guard ring has a depth smaller than adepth of the isolation layer.
 4. The method of claim 1, wherein the wellregion has a depth larger than a depth of the isolation layer.
 5. Themethod of claim 4, wherein a lower portion of the well region surroundsa part of a lower surface of the isolation layer.
 6. The method of claim1, wherein the forming of the guard ring comprises: forming an ionimplantation mask over the substrate to expose the deep well of theopposite side of the isolation layer and a part of the isolation layerbeing in contact with the deep well; and ion-implanting a firstconductive type impurity by using the ion implantation mask as an ionimplantation barrier.
 7. The method of claim 1, wherein the forming ofthe anode electrode and the cathode electrode comprises: depositing ametal layer over a resultant structure including the substrate; forminga metal silicide layer by reacting the substrate with the metal layerthrough a thermal treatment process; and removing a metal layer whichdoes not react in the thermal treatment process.
 8. A method forfabricating a Schottky diode, comprising: forming an isolation layer ina substrate in which a deep well of a second conductive type is formed;forming a well region of a second conductive type in the deep well alongan outer sidewall of the isolation layer to be located at one side ofthe isolation layer; forming a guard ring of a first conductive type inthe deep well along the outer sidewall of the isolation layer to belocated at an opposite side of the isolation layer in such a manner thata part of the guard ring overlaps the isolation layer; and forming ananode electrode over the substrate to be coupled to the deep well andthe guard ring and simultaneously forming a cathode electrode coupled tothe well region over the substrate, wherein a first region of the guardring overlaps with the isolation layer and a second region of the guardring does not overlap with the isolation layer, wherein a width of a topsurface of the first region is different from a width of a top surfaceof the second region, and wherein the width of a top surface of thesecond region is substantially the same as a width of a bottom surfaceof the second region.
 9. The method of claim 8, wherein a n overlappingwidth between the guard ring and the isolation layer is smaller than awidth of the guard ring not overlapping the isolation layer.
 10. Themethod of claim 8, wherein the isolation layer has a ring shape.
 11. Themethod of claim 8, wherein the guard ring has a depth smaller than adepth of the isolation layer on a basis of an upper surface of thesubstrate.
 12. The method of claim 8, wherein the isolation layer has adepth smaller than a depth of the well region on the basis of the uppersurface of the substrate.
 13. The method of claim 12, wherein a lowerportion of the well region surrounds a portion of a lower surface of theisolation layer.
 14. The method of claim 8, wherein the forming of thewell region comprises: forming an ion implantation mask over thesubstrate to expose the deep well of an outer side of the isolationlayer; forming a first impurity region in the deep well by ionimplanting a second conductive type impurity by using the ionimplantation mask as an ion implantation barrier; forming a secondimpurity region on an upper portion of the first impurity region byion-implanting the second conductive type impurity by using the ionimplantation mask as an ion implantation barrier, the second impurityregion having an impurity doping concentration higher than an impuritydoping concentration of the first impurity region; and forming a thirdimpurity region on an upper portion of the second impurity region byion-implanting the second conductive type impurity by using the ionimplantation mask as an ion implantation barrier, the third impurityregion having an impurity doping concentration higher than an impuritydoping concentration of the second impurity region.
 15. The method ofclaim 8, wherein the forming of the anode electrode and the cathodeelectrode comprises: depositing a metal layer over a resultant structureincluding the substrate; forming a metal silicide layer by reacting thesubstrate with the metal layer through a thermal treatment process; andremoving a metal layer which does not react in the thermal treatmentprocess.
 16. The method of claim 8, wherein the width of a top surfaceof the first region is smaller than the width of a top surface of thesecond region.
 17. A method of claim 8, wherein the width of a topsurface of the first region is substantially the same as a width of abottom surface of the first region.